Thermopile



Patented Feb. 27, 1951 THERMOPILE Ferenc Okolicsanyi, Hampstead, London,EnglandV Application August 30, 1945, Serial No. 613,544 In GreatBritain September 1, 1944 (Cl. 13S-4) 1 claim. l

The present invention relates to thermopiles and has for its main objectthe provision of a thermopile capable of giving a current which can beemployed to do useful work.

A further object of the invention is to provide a structure of athermopile which is capable of transferring very large quantities ofheat energy from the hot to the cold junctions and of converting thisinto electrical energy with a reasonable degree of eliiciency. Hitherto,as far as is known, no proposal has been made for a thermopile capableof handling high input energies of the order of many kilowatts.

A still further object of the invention is to provide a thermopile whichcan utilize materials of high specific thermo-electric power andrelatively high electrical resistance and yet yield a current of usefulamperage.

According to the present invention such a thermopile comprises a centraltube, alternating members of different thermo-electric powerssurrounding said tube at least in part, an inner edge adjacent the tubeand an outer edge remote from the tube, and electrically conductingsurfaces arranged to connect the members electrically in series by theiredges so that the thermo-electric current flows outwardly from the innerto the outer edges of one member, and inwardly from the outer to theinner edges of the next.

With such an arrangement, it becomes possible to employ members having alarge effective crosssection at right angles to the electrical andthermal flow. Thus considerable heat energy can be handled without thewhole device heating up to a more or less uniform temperature, and evenwhen it is not desired to handle such large heat energies the structurehas the advantage, for the same reason, that materials of high specificelectrical resistance can be employed.

The invention may be put into practice in various ways, and someexamples of the thermopiles constructed according to the invention willnow be described with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal section of one form of thermopile;

Figure 2 shows a modied and preferred form of the thermopile shown inFigure 1;

Figure 3 shows a cross-section of a thermopile employing cooling ns.

Referring to Figure 1, a central tube I of steel, coated on its outersurface with a thin electrically insulating layer 2 (for example, glassor other vitreous material, sprayed on the outer surface) carries rings3 of cuprous sulphide alternating CJI with electrically insulating ringsof ceramic or refractory material carrying a sprayed coating 5 of copperon one face. Each ring 3 and layer 5 constitute a thermo-couple and areconnected together by aA coating 8 of copper. The various thermo-couplesare separated, either by air spaces 'I as shown, but preferably byinsulating rings occupying these air spaces, and are connected in seriesby further copper coatings f5, as shown. When heat is applied throughthe tube I, the thermo-electric current will ow radially from the inneredge of the ring 3 to its outer edge, through the conducting layer 8,and then back from the outer edge of the layer 5 to its inner edge, andthrough the layer to the next couple, and so on, and is taken ofi' atthe terminals 9, Iii.

Surrounding the thermopile is an annular water jacket formed byconcentric tubes II, I2, an electrically insulating layer I3 beingprovided to prevent short-circuiting of the thermo-couples.

As mentioned above, the use of the insulating rings 4 coated with thecopper layers 5 is necessitated by the low electrical resistance oicopper compared with that of cuprous sulphide. It is preferred toemploy, instead of copper, a material such as the alloy of bismuth andtellurium mentioned above, which has a high negative thermoelectricpower. The electrical resistance of this material is of the same orderas many materials having a high positive thermo-electric power, such asthe intermetallic compound of bismuth and tellurium, so that a structuresuch as that shown in Figure 2 can be employed, in which the rings I5 ofthis alloy replace the copper coated insulating rings 4. The widths ofthe rings in the axial direction are so chosen that the electricalresistance to the thermo-electric current is substantially the same forthe two rings of each thermo-couple, assuming a constant temperaturedifference throughout the length of the thermopile. Also, the rings 3and I5 have a radial thickness less than their axial width. In actualpractice a temperature gradient will exist along the central tube I, andthe width of the rings can be similarly graded so that the ratio of thethermoelectric voltage to the resistance is constant for eachthermo-couple. The rings are separated by insulating discs I 6 and theconnections are made by coatings 6, 8, as in the previous example.

This structure may employ as the positive thermo-electric element, ringsof molybdenum sulphide, which has a very high thermo-electric power, butnormally has an extremely high electrical resistance. I have found,however, that if the material is subject to pressure in a direc tion atright angles to the grain of the material (which has a iiaky structuresimilar to graphite), the electrical resistance is substantiallyreduced. This fact can be taken advantage of by making the rings in sucha way that the grain or layers of material run circumferentially andthen shrinking the steel tube II over the structure so that pressure isexerted in the radial direction. The insulating layers i3 will beproduced in this case by spraying glass over the conducting layer 8prior to the shrinking operation.

The metals may, if desired, be sprayed in known manner on to the surfaceof the tube. Alternatively, the members surrounding the tube may beproduced by the known powderised and sinterising process since this willenable one to overcome the difficulties which arise when using brittlemetals, metal alloys or metal compounds.

It will be understood that in Figures 1 and '2, the Various parts arenot drawn to scale, and, in particular, the various conducting andinsulating layers are shown with exaggerated thickness for the sake ofclarity. Also the steel tubes I and il should be as thin as possibleconsistent with mechanical rigidity.

Many modifications or the structure described above are possible and arewithin the scope of the invention. Figure Y3, for example, shows across-section of thermopile which diiTers in that a central tube I ofsubstantially square instead of circular cross-section is employed, andthat instead of rings surrounding the tube, curved members, one of whichis shown at I 8, embracing only a part of the tube are employed. TheVarious conducting and insulating layers are not shown, as thearrangement of them is substantially the same as in the previousexample. An entirely separate tnermopile is formed on the underside ofthe tube, one of the elements being shown at I9, and the two thermopilescan be corinected in series or parallel as desired. Instead of watercooling, air cooling is employed, each member being provided With acooling iin 2E! for this purpose. As mentioned above such an arrangementcan be used only for low power ratings; for high ratings forcedcirculation of water through the outer jacket by means of a pump isessential to remove the heat sufficiently rapidly, and a radiator ofnormal construction can be included in the cooling circuit.

Iclaim:

A thermopile comprising a central tube, alternately arranged flat ringsof materials of dilerent thermo-electric powers surrounding said tubeand electrically insulated therefrom, said rings having a radialthickness less than their axial width, and electrically conductinglayers arranged to connect the rings electrically in series by theiredges s0 that the thermo-electric current; flows outwardly from theinner to the outer edge of one ring and inwardly from the outer to theinner edge of the next.

FERENC OKOLICSANYI.

REFERENCES CITED The following references are of record inthe le of thispatent:

UNITED STATES PATENTS Number Name Date '775,187 Lyons et al. Nov. 15,1904 1,638,943 Little Aug. 16, 1927 FOREIGN PATENTS Number Country Date627,049 France May 28, 1927 313,602 Great Britain Aug. 28, 1930 '742,364France Dec. 27, 1932

